Sure, these Brazilian historic cities are unique destinations that offer a blend of culture, heritage, and natural beauty. Here are some travel tips for your trip:

Best Time to Visit:
The best time to visit these cities is during the dry season, which is typically from April to September. During this time, the temperatures are cooler which makes sightseeing more enjoyable.

Route and Accessibility:
The trip usually starts from Belo Horizonte, which is accessible by flights from most major cities worldwide. From there, you can rent a car or take a bus to Ouro Preto, Mariana, and Diamantina.

Altitude and Acclimatization:
While these cities are not particularly high in altitude, Ouro Preto is hilly with steep cobblestone streets. Therefore, getting acclimated to walking up and down is beneficial.

Accommodation and Booking:
Hotels, guest houses, and vacation rentals are available in all of these locations. It is advisable to book your accommodations at least a few weeks in advance, especially during holidays and festivals.

Clothing and Essentials:
For daytime, light clothing would be appropriate. However, the temperature can drop significantly at night so bringing a light sweater or jacket would be advisable.

Health and Safety:
In addition to your regular medication, if any, it would be a good idea to have some basic medicines for stomach upsets or motion sickness on hand.

Local Etiquette and Respect:
These cities have a rich history and culture. While photographing public places is generally acceptable, if you wish to photograph individuals, you should ask for permission. Dress modestly in religious places. Brazilians are known for their friendliness, being polite and respectful will be appreciated.

Enjoy your trip and make sure to explore the historical landmarks, stunning architecture, and natural wonders each of these cities has to offer!